5 research outputs found
Interplay between the overlapping ends of tropomyosin and the N terminus of cardiac troponin T affects tropomyosin states on actin
The functional significance of the molecular swivel at the head-to-tail overlapping ends of contiguous tropomyosin (Tm) dimers in striated muscle is unknown. Contractile measurements were made in muscle fibers from transgenic (TG) mouse hearts that expressed a mutant α-Tm (Tm
H276N
). We also reconstituted mouse cardiac troponin T (McTnT) N-terminal deletion mutants, McTnT
1–44
Δ
and McTnT
45–74
Δ
, into muscle fibers from Tm
H276N
. For controls, we used the wild-type (WT) McTnT because altered effects could be correlated with the mutant forms of McTnT. Tm
H276N
slowed crossbridge (XB) detachment rate (
g
) by 19%. McTnT
1–44
Δ
attenuated Ca
2+
-activated maximal tension against Tm
WT
(36%) and Tm
H276N
(38%), but sped
g
only against Tm
H276N
by 35%. The rate of tension redevelopment decreased (17%) only in McTnT
1–44
Δ
+ Tm
H276N
fibers. McTnT
45–74
Δ
attenuated tension (19%) and myofilament Ca
2+
sensitivity (pCa
50
=5.93
vs.
6.00 in the control fibers) against Tm
H276N
, but not against Tm
WT
background. Thus, altered XB cycling kinetics decreased the fraction of strongly bound XBs in McTnT
1–44
Δ
+ Tm
H276N
fibers, whereas diminished thin-filament cooperativity attenuated tension in McTnT
45–74
Δ
+ Tm
H276N
fibers. In summary, our study is the first to show that the interplay between the N terminus of cTnT and the overlapping ends of contiguous Tm effectuates different states of Tm on the actin filament. —Mamidi, R., Michael, J. J., Muthuchamy, M., Chandra, M. Interplay between the overlapping ends of tropomyosin and the N terminus of cardiac troponin T affects tropomyosin states on actin
Deletion of 1–43 amino acids in cardiac myosin essential light chain blunts length dependency of Ca2+ sensitivity and cross-bridge detachment kinetics
The role of cardiac myosin essential light chain (ELC) in the sarcomere length (SL) dependency of myofilament contractility is unknown. Therefore, mechanical and dynamic contractile properties were measured at SL 1.9 and 2.2 μm in cardiac muscle fibers from two groups of transgenic (Tg) mice:
1
) Tg-wild-type (WT) mice that expressed WT human ventricular ELC and
2
) Tg-Δ43 mice that expressed a mutant ELC lacking 1–43 amino acids. In agreement with previous studies, Ca
2+
-activated maximal tension decreased significantly in Tg-Δ43 fibers. pCa
50
(−log
10
[Ca
2+
]
free
required for half maximal activation) values at SL of 1.9 μm were 5.64 ± 0.02 and 5.70 ± 0.02 in Tg-WT and Tg-Δ43 fibers, respectively. pCa
50
values at SL of 2.2 μm were 5.70 ± 0.01 and 5.71 ± 0.01 in Tg-WT and Tg-Δ43 fibers, respectively. The SL-mediated increase in the pCa
50
value was statistically significant only in Tg-WT fibers (
P
< 0.01), indicating that the SL dependency of myofilament Ca
2+
sensitivity was blunted in Tg-Δ43 fibers. The SL dependency of cross-bridge (XB) detachment kinetics was also blunted in Tg-Δ43 fibers because the decrease in XB detachment kinetics was significant (
P
< 0.001) only at SL 1.9 μm. Thus the increased XB dwell time at the short SL augments Ca
2+
sensitivity at short SL and thus blunts SL-mediated increase in myofilament Ca
2+
sensitivity. Our data suggest that the NH
2
-terminal extension of cardiac ELC not only augments the amplitude of force generation, but it also may play a role in mediating the SL dependency of XB detachment kinetics and myofilament Ca
2+
sensitivity
Deletion of 1–43 amino acids in cardiac myosin essential light chain blunts length dependency of Ca 2+
The role of cardiac myosin essential light chain (ELC) in the sarcomere length (SL) dependency of myofilament contractility is unknown. Therefore, mechanical and dynamic contractile properties were measured at SL 1.9 and 2.2 μm in cardiac muscle fibers from two groups of transgenic (Tg) mice: 1) Tg-wild-type (WT) mice that expressed WT human ventricular ELC and 2) Tg-Δ43 mice that expressed a mutant ELC lacking 1–43 amino acids. In agreement with previous studies, Ca(2+)-activated maximal tension decreased significantly in Tg-Δ43 fibers. pCa(50) (−log(10) [Ca(2+)](free) required for half maximal activation) values at SL of 1.9 μm were 5.64 ± 0.02 and 5.70 ± 0.02 in Tg-WT and Tg-Δ43 fibers, respectively. pCa(50) values at SL of 2.2 μm were 5.70 ± 0.01 and 5.71 ± 0.01 in Tg-WT and Tg-Δ43 fibers, respectively. The SL-mediated increase in the pCa(50) value was statistically significant only in Tg-WT fibers (P < 0.01), indicating that the SL dependency of myofilament Ca(2+) sensitivity was blunted in Tg-Δ43 fibers. The SL dependency of cross-bridge (XB) detachment kinetics was also blunted in Tg-Δ43 fibers because the decrease in XB detachment kinetics was significant (P < 0.001) only at SL 1.9 μm. Thus the increased XB dwell time at the short SL augments Ca(2+) sensitivity at short SL and thus blunts SL-mediated increase in myofilament Ca(2+) sensitivity. Our data suggest that the NH(2)-terminal extension of cardiac ELC not only augments the amplitude of force generation, but it also may play a role in mediating the SL dependency of XB detachment kinetics and myofilament Ca(2+) sensitivity
Interplay between the overlapping ends of tropomyosin and the N terminus of cardiac troponin T affects tropomyosin states on actin
The functional significance of the molecular swivel at the head-to-tail overlapping ends of contiguous tropomyosin (Tm) dimers in striated muscle is unknown. Contractile measurements were made in muscle fibers from transgenic (TG) mouse hearts that expressed a mutant α-Tm (Tm(H276N)). We also reconstituted mouse cardiac troponin T (McTnT) N-terminal deletion mutants, McTnT(1–44)(Δ) and McTnT(45–74)(Δ), into muscle fibers from Tm(H276N). For controls, we used the wild-type (WT) McTnT because altered effects could be correlated with the mutant forms of McTnT. Tm(H276N) slowed crossbridge (XB) detachment rate (g) by 19%. McTnT(1–44)(Δ) attenuated Ca(2+)-activated maximal tension against Tm(WT) (36%) and Tm(H276N) (38%), but sped g only against Tm(H276N) by 35%. The rate of tension redevelopment decreased (17%) only in McTnT(1–44)(Δ) + Tm(H276N) fibers. McTnT(45–74)(Δ) attenuated tension (19%) and myofilament Ca(2+) sensitivity (pCa(50)=5.93 vs. 6.00 in the control fibers) against Tm(H276N), but not against Tm(WT) background. Thus, altered XB cycling kinetics decreased the fraction of strongly bound XBs in McTnT(1–44)(Δ) + Tm(H276N) fibers, whereas diminished thin-filament cooperativity attenuated tension in McTnT(45–74)(Δ) + Tm(H276N) fibers. In summary, our study is the first to show that the interplay between the N terminus of cTnT and the overlapping ends of contiguous Tm effectuates different states of Tm on the actin filament. —Mamidi, R., Michael, J. J., Muthuchamy, M., Chandra, M. Interplay between the overlapping ends of tropomyosin and the N terminus of cardiac troponin T affects tropomyosin states on actin